Rotary engine casing

ABSTRACT

A rotary engine casing having at least one end wall of an internal cavity for a rotor including a seal-engaging plate sealingly engaging the peripheral wall to partially seal the internal cavity and a member mounted adjacent the seal-engaging plate outside of the internal cavity. The member and seal-engaging plate having abutting mating surfaces which cooperate to define between them at least one fluid cavity communicating with a source of liquid coolant. When the casing includes a plurality of rotor housings, the end wall may be between rotor housings. A method of manufacturing a rotary engine casing is also discussed.

TECHNICAL FIELD

The application relates generally to rotary engines, and moreparticularly, to engine casings for such engines.

BACKGROUND OF THE ART

In certain rotary engines, liquid cooling is provided in the side or endcasings, and when multiple rotors are present, in the intermediatecasing(s). In these engine casings, fluid cavities are provided to coolthe rotor housings. However, the manufacturing of such engine casingscan be complex and limited to specific manufacturing methods, such ascasting. Moreover, since the casings have surfaces in sliding contactwith the rotating rotors, wear and damage is inevitable. Yet, because ofthe cooling passages these can be expensive components to replace.

SUMMARY

In one aspect, there is provided a rotary engine casing comprising firstand second axially spaced apart end walls interconnected by a peripheralwall, the first end wall, second end wall and peripheral wall togetherenclosing an internal cavity configured to sealingly engage a rotorrotatable therein, at least the first end wall including a seal-engagingplate sealingly engaging the peripheral wall to partially seal theinternal cavity and a member mounted adjacent the seal-engaging plateoutside of the internal cavity, the member and seal-engaging platehaving abutting mating surfaces, the mating surfaces cooperating todefine between them at least one fluid cavity communicating with asource of liquid coolant, the at least one fluid cavity configured to inuse cool the rotor.

In another aspect, there is provided a rotary engine casing comprising:a plurality of axially spaced end walls; two end-casing sections locatedat opposite ends of the rotary engine casing and each including arespective one of the end walls; and

a central-casing section mounted between the two end-casing sections,the central-casing section comprising: a plurality of rotor housingseach including a peripheral wall of a respective internal cavity forreceiving a respective rotor, each peripheral wall cooperating with twoof the end walls to enclose the respective internal cavity; and anintermediate section mounted between each adjacent ones of the rotorhousings, each intermediate section including a first seal-engagingplate sealingly engaging the peripheral wall of a first of the adjacentones of the rotor housings to partially seal the internal cavitythereof, a second seal-engaging plate sealingly engaging the peripheralwall of a second of the adjacent ones of the rotor housings to partiallyseal the internal cavity thereof, and a member mounted between the firstand second seal-engaging plates, the member and first seal-engagingplate having abutting first mating surfaces cooperating to definebetween them at least one first fluid cavity communicating with a sourceof liquid coolant, the member and second seal-engaging plate havingabutting second mating surfaces the mating surfaces cooperating todefine between them at least one second fluid cavity communicating withthe source of liquid coolant.

In a further aspect, there is provided a method of manufacturing arotary engine casing, the method comprising: manufacturing twoend-casing sections including a first part of a fluid path forcirculating a cooling fluid; manufacturing a central-casing sectiondefining at least one internal cavity for receiving a rotor and a secondpart of the fluid path; wherein at least one of the manufacturing of thetwo end-casing sections and of the manufacturing of the central-casingsection includes: manufacturing a member having a first mating surface,manufacturing a seal-engaging plate having a second mating surface, andmachining at least one surface depression on at least one of the firstand second mating surfaces, the at least one surface depression in fluidcommunication with the fluid path; and assembling the central-casingsection between the two end-casing sections, including connecting thefirst and second parts of the fluid path, and assembling the member withthe seal-engaging plate by abutting the first and second mating surfacessuch that the at least one surface depression defines a fluid cavity incommunication with the fluid path for circulating a cooling fluidtherein.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a rotary internalcombustion engine in accordance with a particular embodiment;

FIG. 2 is a schematic side view of a rotor engine casing in accordancewith a particular embodiment;

FIG. 3 is an exploded tridimensional view of the engine casing shown inFIG. 2;

FIG. 4 is a schematic tridimensional view of a member and aseal-engaging plate of the engine casing of FIG. 2; and

FIG. 5 is a schematic cross-sectional view of the engine casing shown inFIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1, a rotary engine 120 according to a particularembodiment is shown. The rotary engine is a Wankel engine and comprisesa casing 10 having at least one internal cavity 32 (only one beingvisible in FIG. 1), each internal cavity 32 being defined by two axiallyspaced apart end walls 80 interconnected by a peripheral wall 34. Eachinternal cavity 32 has a profile defining two lobes, which is preferablyan epitrochoid. A rotor 82 is received within each internal cavity 32.The rotor defines three circumferentially-spaced apex portions 84, and agenerally triangular profile with outwardly arched sides. The apexportions 84 are in sealing engagement with the inner surface of theperipheral wall 34 of the casing 10 to form three working chambers 94between the rotor 82 and the casing 10.

The rotor 82 is engaged to an eccentric portion 86 of a shaft 88 toperform orbital revolutions within the internal cavity 32. The shaft 88performs three rotations for each orbital revolution of the rotor 82.The geometrical axis 90 of the rotor 82 is offset from and parallel tothe axis 92 of the casing 10. During each orbital revolution, eachchamber 94 varies in volume and moves around the internal cavity 32 toundergo the four phases of intake, compression, expansion and exhaust.

An intake port 96 is provided through the peripheral wall 34 forsuccessively admitting compressed air into each working chamber 94. Anexhaust port 98 is also provided through the peripheral wall 34 forsuccessively discharging the exhaust gases from each working chamber 94.Passages 100 for a glow plug, spark plug or other ignition element, aswell the fuel injectors are also provided through the peripheral wall34. Alternately, the intake port 96, the exhaust port 98 and/or thepassages 100 may be provided through one of the end walls 80 of thecasing 10; and/or, the ignition element and a pilot fuel injector maycommunicate with a pilot subchamber (not shown) defined in the rotorcasing 10 and communicating with the internal cavity 32 for providing apilot injection. The pilot subchamber may be for example defined in aninsert (not shown) received in the peripheral wall 34.

In a particular embodiment, the fuel injectors are common rail fuelinjectors, and communicate with a source of heavy fuel (e.g. diesel,kerosene (jet fuel), equivalent biofuel), and deliver the heavy fuelinto the engine(s) such that the combustion chamber is stratified with arich fuel-air mixture near the ignition source and a leaner mixtureelsewhere.

For efficient operation the working chambers 94 are sealed, for exampleby spring-loaded apex seals 102 extending from the rotor 82 to engagethe peripheral wall 34, and spring-loaded face or gas seals 104 and endor corner seals 106 extending from the rotor 82 to engage the end walls80. The rotor 82 also includes at least one spring-loaded oil seal ring108 biased against the end wall 80 around the bearing for the rotor 82on the shaft eccentric portion 86. Alternately, the oil seal ring(s) maybe provided in the end walls 80 to engage the rotor 82.

In a particular embodiment which may be particularly but not exclusivelysuitable for low altitude, each Wankel engine has a volumetric expansionratio of from 5 to 9, and operates following the Miller cycle, with avolumetric compression ratio lower than the volumetric expansion ratio,for example by having the intake port located closer to the top deadcenter (TDC) than an engine where the volumetric compression andexpansion ratios are equal or similar. Alternately, each Wankel enginemay operate with similar or equal volumetric compression and expansionratios.

It is understood that other configurations are possible for the engine120. The configuration of the engine 120, e.g. placement of ports,number and placement of seals, number of fuel injectors, etc., may varyfrom that of the embodiment shown.

Referring to FIG. 2, in a particular embodiment the rotary engine casing10 defines two axially spaced internal cavities each receiving one oftwo rotors engaged to a common shaft. The engine casing 10 includesmultiple assembled casing sections which cooperate to define theinternal cavities and contain the rotors and shaft, and includebearing-support features, and cooling and lubrication passages, asdetailed further below.

In the particular embodiment shown in FIG. 2, the engine casing 10includes two end-casing sections 12, located at opposite ends of theengine casing 10, and each defining an end wall 80 of a respective oneof the internal cavities 32, and a central-casing section 14 mountedbetween the two end-casing sections 12. The central-casing section 14includes two rotor housings 30 each defining the peripheral wall 34 of arespective internal cavity 32, and an intermediate section 38 definingthe end wall 80 extending between both internal cavities 32 to separatesand seal the internal cavities 32. Each end-casing section 12 is splitto allow separation of the end-casing section 12 into two sub-parts 16,20 and the intermediate section 38 is split into three sub-parts 40, 46.Advantageously, the sub-parts can be machined, dowelled and/or boltedtogether and kept as a semi-permanent sub-assembly to ease in theprocess of engine assembly. Although the casing 10 is described hereinwith the two end-casing sections 12 and the intermediate section 38(i.e. all end walls 80) having a split configuration, it is understoodthat in an alternate embodiment, only one or two of the end-casingsections 12 and intermediate section 38 may have a split configuration.

The central-casing section 14 shown in FIG. 2 has two rotor housings 30separated by one intermediate section 38, to receive two rotors. In analternate embodiment, the engine 120 can have any other adequate numberof rotors and accordingly the central-casing section 14 can have acorresponding number of rotor housings 30. If only one rotor housing 30is provided, the intermediate section 38 is omitted and, if multiplerotor housings 30 are provided, each pair of rotor housings 30 isseparated by an intermediate section 38.

Referring to FIG. 3, each end-casing section 12 includes an end-casingmember 16 having a mating surface 18. The end-casing member 16 is an endportion delimiting the axial boundary of the engine casing 10.

Each end-casing section 12 also includes a seal-engaging plate 20connected to the end-casing member 16. The seal-engaging plate 20 has amating surface 22 abutted to the mating surface 18 of the end-casingmember 16, and a sliding surface 24, which in a particular embodiment isa hardened surface, facing away from the end-casing member 16 anddefining a surface of the respective internal cavity 32. Theseal-engaging plate 20 sealingly engages the peripheral wall 34 definedby the adjacent rotor housing 30 to partially seal the correspondinginternal cavity. In use, the face seals 104 of the rotor 82 (see FIG. 1)thus engage the sliding surfaces 24. The sliding surfaces 24 can haveany surface finish suitable for sealing engagement with the face seals104.

Each end-casing member 16 has an aperture 17 defined therethrough toreceive a bearing housing (not shown) supporting the engine shaft 88(FIG. 1). Similarly, each seal-engaging plate 20 has an aperture 19defined therethrough concentrically with the aperture of the associatedend-casing member 16, sized to receive the engine shaft 88 therethrough.

As can be best seen in FIG. 5, the end-casing member 16 also include oilscavenge cavities 21 defined in the mating surface 18 around theaperture, and oil circulation passages 23 in fluid communication withthe scavenge cavities and with an oil reservoir 58 forming part of anoil path providing oil or other lubricating fluid circulation throughthe engine 120, including the central-section 14.

Still referring to FIG. 5, each end-casing section 12 also includes atleast one fluid cavity 26 in fluid communication with a source of liquidcoolant (e.g. water) through a cooling fluid path of the engine casing10, for cooling the end-casing section 12. The cooling fluid pathincludes an inlet and an outlet which may be defined in one of theend-casing sections 12, and is in fluid communication with anappropriate cooler (not shown).

Each end-casing fluid cavity 26 is located between the mating surfaces18, 22 and is defined by surface depression(s) 28 formed on one or bothof the mating surfaces 18, 22. In the particular embodiment shown inFIGS. 3-5, the end-casing fluid cavity 26 includes multiple cooperatingsurface depressions 28 formed on the mating surfaces 18, 22. The surfacedepressions 28 are sized and positioned to allow adequate cooling of theengine casing 10. As can be best seen in FIG. 4, complementary surfacedepressions 28 are defined in each of the mating surfaces 18, 22 andcooperate to form the end-casing fluid cavities 26. The end-casing fluidcavity 26 can have any configuration suitable for circulating a coolingfluid therein. In the particular embodiment shown, the fluid pathincludes a plurality of apertures 36 defined across the engine casing10, including the seal-engaging plate 20 and central-casing section 14,in fluid communication with the fluid cavities 26, such that the coolingfluid can circulate within the cavities 26 and through the varioussections of the engine casing 10. In the embodiment shown, the apertures36 extend axially across seal-engaging plate 20 and central-casingsection 14, from the fluid cavities 26 of one of the end-casing sections12 to the fluid cavities 26 of the other of the end-casing sections 12.It is understood that any other adequate type of fluid communication mayalternately be used.

In an alternate embodiment which is not shown, the surface depression(s)28 of the end-casing fluid cavity 26 is/are located only on the matingsurface 18 of the end-casing member 16. In that case, the mating surface22 of the seal-engaging plate 20 does not include surface depressions.In another alternate embodiment which is not shown, the surfacedepression(s) 28 of the end-casing fluid cavity 26 is/are located on themating surface 22 of the seal-engaging plate 20. In that case, themating surface 18 does not include surface depressions. It is alsounderstood that any combination of fluid cavities defined by depressionsin only one of the mating surfaces 18, 22 and defined by depression inboth of the mating surfaces 18, 22 can be used.

In the embodiment shown, and as can be seen more clearly in FIG. 5, thetwo end-casing sections 12 have different configurations and eachend-casing sections 12 has a different number of end-casing fluidcavities 26. Alternately, the two end-casing sections 12 may havesimilar fluid cavities 26.

The end-casing member 16 has a thickness greater than a thickness of theseal-engaging plate 20. In a particular embodiment, the seal-engagingplate 20 has a thickness of 0.25 times that of the end-casing member 16;other relative dimensions may alternately be used.

Referring back to FIG. 3, the central-casing section 14 of theparticular embodiment shown includes two rotor housing 30 each defininga respective internal cavity 32 for receiving a respective rotor 82(shown in FIG. 1). Each adjacent ones of the rotor housings 30 areseparated by an intermediate section 38. The intermediate section 38 hassimilar functionalities as the end-casing section 12 described above andseparates adjacent rotor housings 30 in multi-rotor engines.

The intermediate section 38 includes an intermediate member 40 which hasopposite, parallel mating surfaces 42. The intermediate section 38 alsoincludes a pair of intermediate seal-engaging plates 46 connected to theintermediate member 40. Each intermediate seal-engaging plate 46 has amating surface 48 abutted to a respective one of the mating surfaces 42of the intermediate member 40 and, a sliding surface 50, which in aparticular embodiment is a hardened sliding surface, facing away fromthe intermediate member 40 and defining a surface of the respectiveinternal cavity 32. The seal-engaging plates 46 each sealingly engagethe peripheral wall 34 defined by the adjacent rotor housing 30 topartially seal the corresponding internal cavity.

As can also be seen in FIG. 5, the intermediate member 40 has anaperture 41 defined therethrough concentrically with the apertures 17,19 of the end-casing sections 12 to the engine shaft 88 therethrough;although not shown, the aperture 41 could also be sized to receive abearing housing, particularly but not exclusively for engines includingmore than two rotors. Similarly, each seal-engaging plate 46 has anaperture 47 defined therethrough concentrically with the aperture of theintermediate member 40, sized to also receive the engine shaft 88therethrough. The intermediate member 40 includes an oil scavengepassage 25 communicating with the aperture 41 and with the oil reservoir58.

The intermediate section 38 also includes at least one intermediatefluid cavity 52 in fluid communication with the fluid path of the enginecasing 10, for cooling the rotor housing 30. Each intermediate fluidcavity 52 is located between the intermediate member 40 and theintermediate seal-engaging plates 46. Each intermediate fluid cavity 52is defined by a surface depression 54 formed on the mating surface 48 ofthe respective seal-engaging plate 46, while the mating surfaces 42 ofthe intermediate member 40 are free of depressions.

In an alternate embodiment which is not shown, one or more of theintermediate fluid cavities 52 may be defined by depressions in themating surface 42 of the intermediate member 40, alone or in combinationwith a complementary depression in the mating surface 48 of thecorresponding seal-engaging plate 46. It is also understood that anycombination of fluid cavities defined by depressions in only one of theabutting mating surfaces 42, 48 and defined by depression in both of theabutting mating surfaces 42, 48 can be used.

The intermediate fluid cavity 52 can have any configuration suitable forcirculating a cooling fluid therein. In the particular embodiment shown,the apertures 36 of the fluid path defined across the engine casing 10extend through the seal-engaging plates 46 and the intermediate member40, in fluid communication with the intermediate fluid cavities 52 toconnect the fluid cavities 52 to the fluid path. It is understood thatany other adequate type of fluid communication may alternately be used.

In the illustrated embodiment, the intermediate fluid cavities 52 areshaped differently from the end-casing fluid cavities 26, and arepositioned along different circumferential portions of the engine 120.The shape and position of the fluid cavities can be optimized based onengine operating conditions and/or configuration. In the embodimentshown, the intermediate fluid cavities 52 are concentrated along thecircumferential portion of the rotor housing 30 where combustion occurs.

In the embodiment shown, and as can be seen more clearly in FIG. 5, thetwo seal-engaging plates 46 have different configurations and differentintermediate fluid cavities 52 are defined on each side of theintermediate member 40. Alternately, the two sides of the intermediatemember 40 may have similar fluid cavities 52.

The intermediate member 40 has a thickness greater than a thickness ofthe seal-engaging plates 46. In a particular embodiment, theseal-engaging plates 46 each have a thickness of 0.5 times that of theintermediate member 40; other relative dimensions may alternately beused.

In a particular embodiment, the engine casing 10 allows for replacementof the seal-engaging plates 20, 46 without replacing the entireend-casing section 12 or the entire central-casing section 14, forexample in case of damage to the sliding surfaces 24, 50.

As shown in FIG. 5, fasteners such as circumferentially spaced bolts 60(only one of which is shown) interconnect the sections to form theengine casing 10.

In a particular embodiment, the fluid cavities 26, 52 of the enginecasing 10 are created by forming the fluid cavities on the matingsurfaces of the engine casing sections. Advantageously, more economicaltechniques may become available, such as machining.

In a particular embodiment, manufacturing of the rotary engine casing 10includes manufacturing a member having a first mating surface such asend-casing member 16 and/or intermediate member 40, and a seal-engagingplate having a second mating surface such as seal-engaging plate 20and/or intermediate seal-engaging plate 46. The surface depression(s)can then be machined on at least one of the mating surfaces to form thefluid cavity. In a particular embodiment, the method includes formingcorresponding depressions on both mating surfaces to form the fluidcavity. Once the depressions are formed the member is assembled with theseal-engaging plate such that the surface depression defines a fluidcavity in communication with the fluid path for circulating a coolingfluid therein. The member and the seal-engaging plate are connectedthrough abutment of the first and second mating surfaces. In aparticular embodiment, this includes dowelling and/or bolting the memberwith the seal-engaging plate in a semi-permanent sub-assembly.

In a particular embodiment, the end-casing members 16, seal-engagingplates 20, rotor housings 30, seal-engaging plates 20 and 46intermediate member(s) 40 are made of a same material; alternately,different materials may be used.

In a particular embodiment, the split casing sections allow to ease theengine casing 10 assembly process. In such an embodiment, it is simplerand more economical to form the fluid cavities as compared to othermanufacturing techniques, such as casting.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Modifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

1. A rotary engine casing comprising first and second axially spacedapart end walls interconnected by a peripheral wall, the first end wall,second end wall and peripheral wall together enclosing an internalcavity configured to sealingly engage a rotor rotatable therein, atleast the first end wall including a seal-engaging plate sealinglyengaging the peripheral wall to partially seal the internal cavity and amember mounted adjacent the seal-engaging plate outside of the internalcavity, the member and seal-engaging plate having abutting matingsurfaces, the mating surfaces cooperating to define between them atleast one fluid cavity communicating with a source of liquid coolant,the at least one fluid cavity configured to in use cool the rotor. 2.The rotary engine casing as defined in claim 1, wherein the casingincludes two axially spaced apart end-casing sections located atopposite ends of the rotary engine casing and a central-casing sectionmounted between and connected to the two end-casing sections, thecentral-casing section including the peripheral wall, and the first endwall located in one of the end-casing sections.
 3. The rotary enginecasing as defined in claim 1, wherein said at least the first end wallincludes the first and second end walls.
 4. The rotary engine casing asdefined in claim 1, wherein the member has a thickness greater than athickness of the seal-engaging plate.
 5. The rotary engine casing asdefined in claim 1, wherein the mating surfaces include complementarydepressions cooperating to form the at least one fluid cavity.
 6. Therotary engine casing as defined in claim 1, wherein one of the matingsurfaces includes at least one depression cooperating with the other ofthe mating surfaces to form the at least one fluid cavity.
 7. The rotaryengine casing as defined in claim 2, wherein the central-casing sectionincludes at least one fluid cavity in fluid communication with the atleast one fluid cavity defined between the mating surfaces.
 8. Therotary engine casing as defined in claim 2, wherein the central-casingsection has a plurality of apertures extending therethrough incommunication with the at least one fluid cavity.
 9. The rotary enginecasing as defined in claim 1, wherein the internal cavity is a firstinternal cavity, the peripheral wall is a first peripheral wall, and theseal-engaging plate is a first seal-engaging plate, the casing furthercomprising a third end wall and a second peripheral wall, the first endwall, third end wall and second peripheral wall together enclosing asecond internal cavity configured to sealingly engage an additionalrotor rotatable therein, the first and second internal cavitiesseparated by the first end wall, the first end wall including a secondseal-engaging plate sealingly engaging the second peripheral wall topartially seal the second internal cavity, the member located betweenthe first and second seal-engaging plates, the member and secondseal-engaging plate having abutting mating surfaces cooperating todefine between them at least one additional fluid cavity communicatingwith the source of liquid coolant.
 10. The rotary engine casing asdefined in claim 9, wherein the first and second seal-engaging plateseach have a thickness smaller than a thickness of the member.
 11. Therotary engine casing as defined in claim 9, wherein each of the at leastone fluid cavity is defined by a respective depression formed in themating surface of the first seal-engaging plate, and each of the atleast one additional fluid cavity is defined by a respective depressionformed in the mating surface of the second seal-engaging plate.
 12. Arotary engine casing comprising: a plurality of axially spaced endwalls; two end-casing sections located at opposite ends of the rotaryengine casing and each including a respective one of the end walls; anda central-casing section mounted between the two end-casing sections,the central-casing section comprising: a plurality of rotor housingseach including a peripheral wall of a respective internal cavity forreceiving a respective rotor, each peripheral wall cooperating with twoof the end walls to enclose the respective internal cavity; and anintermediate section mounted between each adjacent ones of the rotorhousings, each intermediate section including a first seal-engagingplate sealingly engaging the peripheral wall of a first of the adjacentones of the rotor housings to partially seal the internal cavitythereof, a second seal-engaging plate sealingly engaging the peripheralwall of a second of the adjacent ones of the rotor housings to partiallyseal the internal cavity thereof, and a member mounted between the firstand second seal-engaging plates, the member and first seal-engagingplate having abutting first mating surfaces cooperating to definebetween them at least one first fluid cavity communicating with a sourceof liquid coolant, the member and second seal-engaging plate havingabutting second mating surfaces the mating surfaces cooperating todefine between them at least one second fluid cavity communicating withthe source of liquid coolant.
 13. The rotary engine casing as defined inclaim 12, wherein the member has a thickness greater than a thickness ofeach of the seal-engaging plates.
 14. The rotary engine casing asdefined in claim 12, wherein each of the at least one first fluid cavityis defined by a respective depression formed in the mating surface ofthe first seal-engaging plate, and each of the at least one second fluidcavity is defined by a respective depression formed in the matingsurface of the second seal-engaging plate.
 15. The rotary engine casingas defined in claim 12, wherein each end-casing section includes atleast one fluid cavity in fluid communication with the at least onefirst fluid cavity and with the at least one second fluid cavity. 16.The rotary engine casing as defined in claim 12, wherein the respectiveend wall of each end-casing section includes an end-casing seal-engagingplate sealingly engaging the peripheral wall of a respective one of therotor housings to partially seal the internal cavity thereof and anend-casing member mounted adjacent the end-casing seal-engaging plateoutside of the internal cavity, the end-casing member and end-casingseal-engaging plate having abutting mating surfaces cooperating todefine between them at least one additional fluid cavity communicatingwith the source of liquid coolant.
 17. A method of manufacturing arotary engine casing, the method comprising: manufacturing twoend-casing sections including a first part of a fluid path forcirculating a cooling fluid; manufacturing a central-casing sectiondefining at least one internal cavity for receiving a rotor and a secondpart of the fluid path; wherein at least one of the manufacturing of thetwo end-casing sections and of the manufacturing of the central-casingsection includes: manufacturing a member having a first mating surface,manufacturing a seal-engaging plate having a second mating surface, andmachining at least one surface depression on at least one of the firstand second mating surfaces, the at least one surface depression in fluidcommunication with the fluid path; and assembling the central-casingsection between the two end-casing sections, including connecting thefirst and second parts of the fluid path, and assembling the member withthe seal-engaging plate by abutting the first and second mating surfacessuch that the at least one surface depression defines a fluid cavity incommunication with the fluid path for circulating a cooling fluidtherein.
 18. The method as defined in claim 17, wherein machining the atleast one surface depression on at least one of the first and secondmating surfaces includes machining complementary depressions on thefirst and second mating surfaces.
 19. The method as defined in claim 17,wherein manufacturing of the two end-casing sections and themanufacturing of the central-casing section both include manufacturingthe member, manufacturing the seal-engaging plate and machining the atleast one surface depression.
 20. The method as defined in claim 17,wherein the member is manufactured with a thickness greater than that ofthe seal-engaging plate.